PM / Wakeup: Fix initialization of wakeup-related device sysfs files

It turns out that some PCI devices are only found to be
wakeup-capable during registration, in which case, when
device_set_wakeup_capable() is called, device_is_registered() already
returns 'true' for the given device, but dpm_sysfs_add() hasn't been
called for it yet.  This leads to situations in which the device's
power.can_wakeup flag is not set as requested because of failing
wakeup_sysfs_add() and its wakeup-related sysfs files are not
created, although they should be present.  This is a post-2.6.38
regression introduced by commit cb8f51bd
(PM: Do not create wakeup sysfs files for devices that cannot wake
up).

To work around this problem initialize the device's power.entry
field to an empty list head and make device_set_wakeup_capable()
check if it is still empty before attempting to add the devices
wakeup-related sysfs files with wakeup_sysfs_add().  Namely, if
power.entry is still empty at this point, device_pm_add() hasn't been
called yet for the device and its wakeup-related files will be
created later, so device_set_wakeup_capable() doesn't have to create
them.
Reported-and-tested-by: Tino Keitel <tino.keitel@tikei.de>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/base/power/main.c

@@ -63,6 +63,7 @@ void device_pm_init(struct device *dev)
 	dev->power.wakeup = NULL;
 	spin_lock_init(&dev->power.lock);
 	pm_runtime_init(dev);
+	INIT_LIST_HEAD(&dev->power.entry);
 }
 
 /**

drivers/base/power/wakeup.c

@@ -258,7 +258,7 @@ void device_set_wakeup_capable(struct device *dev, bool capable)
 	if (!!dev->power.can_wakeup == !!capable)
 		return;
 
-	if (device_is_registered(dev)) {
+	if (device_is_registered(dev) && !list_empty(&dev->power.entry)) {
 		if (capable) {
 			if (wakeup_sysfs_add(dev))
 				return;